This disclosure relates generally to the field of inserting conduit such as casing or liners in wellbores having extended lateral displacement from the wellbore surface location, e.g., highly inclined or horizontal wellbores.
“Extended reach” wellbore drilling enables drilling a wellbore and extended lateral (horizontal) displacement from a wellbore's surface location. Extended reach wellbores may be used, for example, to gain access to subsurface reservoirs where it is necessary for regulatory and/or environmental reasons that the wellbore's surface location cannot be proximate the subsurface reservoir. Other uses for extended reach wellbores may be to expose a long section of fractured or other hydrocarbon productive formation having relatively horizontal geologic structure.
It is known in the art to insert a casing or liner in such extended reach wellbores.
Inserting a casing or liner may be facilitated by using casing centralizers at spaced apart locations along the casing or liner to limit frictional contact between the casing or liner and the wall of the wellbore. In some cases, using centralizers is inadequate because of the length of the casing or liner to be inserted into the wellbore. In such cases, even with centralizers, there may be sufficient friction between the centralizers or the conduit and the wellbore wall as to make insertion of the conduit (casing or liner) impracticable.
It is also known in the art to insert the casing or liner in the wellbore while it is air filled. Air filling causes the casing or liner to be buoyant in the fluid filling the wellbore. After the casing or liner is inserted to the longitudinal end of the wellbore, various fluids may be pumped into the casing or liner as part of the process of cementing the casing or liner within the wellbore. Cement is eventually pumped as a slurry through the casing or liner and exits through appropriate valves and other equipment at the longitudinal distal end, eventually being displaced into the annular space (“annulus”) between the casing or liner and the wellbore wall. When the cement sets, it may form an impermeable barrier to hydraulically isolate formations from each other and help maintain the mechanical integrity of the wellbore.
Using air to provide buoyancy to run a casing or liner in an extended reach wellbore may have some risk, depending on the trajectory of the wellbore. It is possible under some conditions for air to become trapped in the casing or liner. As fluid is pumped into the casing or liner to begin the cementing process, trapped air can become compressed. When the compressed air is released by opening of the equipment at the bottom of the casing or liner, the pressure may result in dangerous well pressure control conditions.